Tires are occasionally punctured by hard objects, such as nails, stones and so on, on road. Flattening of the tires is resulted due to air-leaking through the puncture and may cause serious accident and severe physical injure to the drivers. Liquid tire sealant products can be used for sealing punctures temporarily when the tires are in operation. This provides an emergency measure for drivers to continue the journey and seek for help even after the tire is punctured, which is especially important for vehicles on highway.
In general, a liquid tire sealant mainly consists of sealing materials, a tackifier and a solvent with an anti-freezing agent. The common sealing materials include the latex, the butyl rubber and various particulates. Tackifiers are chemicals used for increasing the tackiness. A common tackifier used for the tire sealant is the resin compound. Anti-freezing agent, such as the ethylene glycol and the propylene glycol, is used to lower the freezing point of the tire sealant in order to prevent the sealant from freezing at a low temperature operating environment.
Various types of the liquid tire sealant are developed in past decades. In the early stage of the tire sealant development, the most common type, such as but not limited to the inventions of EP 1382654A1, U.S. Pat. Nos. 6,992,119 B2 and 0,142,420 A1, is mainly composed of the butyl rubber and/or the latex emulsion for sealing purpose. The drawbacks of these compositions include their unstable performance (i.e. short shelf-life), odour problem and difficulty to clean up after application.
U.S. Pat. Nos. 4,337,322 and 4588758 describe the further development of the tire sealant. These patents disclose the use of the asbestos fiber, the ethylene glycol and the detergent as main components in the valve-open type sealant. But it is well known that the asbestos fiber is carcinogenic whereas the ethylene glycol is toxic to the environment.
In light of the environmental concerns, a non-petroleum based tire sealant is disclosed in U.S. Pat. No. 5,059,636, and the formulation of this patent includes the ground rubber, the wheat flour and the sodium nitrite. But the drawback of the patent is that the valve core needed to be removed before applying the sealant and it means that the sealant composition in this invention is a valve-open type sealant.
Then a sealant composition based on a mechanism called “log-jam” has received more attention. The “log-jam” mechanism means that particles in the liquid medium accumulate and block at a puncture when the liquid sealant composition flow through the puncture driven by the pressure difference between the inner and outer side of the punctured tire. Each of U.S. Pat. Nos. 5,772,747 and 5,856,376 discloses a sealant composition based on the “log-jam” mechanism, however, the sealant compositions are still valve-open type sealants.
In U.S. Pat. No. 6,013,697, the bentonite clay and the mica are used as the main constituents in the disclosed formulation. These particulates fill the puncture voids and form a clog to prevent a further air leak. The sealant composition disclosed by this patent is a valve-through type sealant that the valve core doesn't need to be removed before applying the sealant composition. The sealant composition is convenient to use, environmentally safe and has a quick sealing performance. However, settling and flocculation of clay platelets are the main issues for this sealant composition.
Other sealant compositions, such as but not limited to U.S. Pat. Nos. 0,077,391 A1, 0129464 A1, 2007/0203260, International Patent WO 2008/022402 A1 and PCT/AU2008/001499, are based on the log jam mechanism and have a lot of innovations on formulations. Advantages of this type of tire sealant include the ease of cleaning after application, free of malodor and longer shelf life. However, this type of tire sealant suffers from a relatively poor sealing performance.
In addition to the “log-jam” mechanism, another type of sealant is based on tackified latex suspension. The latex suspension is a highly viscous liquid that could firmly adhere on the puncture wall and eventually block the air leaking channel. However, disadvantages of the latex-based sealant composition are difficulty to clean after usage, problematic sticky nature, irritation to eyes and skins, use of volatile organic compounds and so on.